Other notable diamonds found in the mine include a 25.5 carat Cullinan blue diamond, found in 2013 and sold for $16.9 million, and a diamond found in 2008, known as the Star of Josephine, which was sold for $9.49 million.

Diamonds from both the Cullinan mine in South Africa and the Williamson facilities in Tanzania, both owned by Petra, have been displayed at London's Buckingham Palace and are regarded as among the rarest and most valuable in the world.

The 1905 Cullinan Diamond has been cut into two stones—the First Star of Africa and the Second Star of Africa—and form part of Britain's Crown Jewels held in the Tower of London.

Dippenaar said the company would decide what to do with the diamond in the next week.